1. Field of the Invention
The present invention relates to an exhaust pump, a communicating pipe, and an exhaust system, and in particular to an exhaust pump, a communicating pipe, and an exhaust system that prevent particles from entering a processing chamber of a substrate processing apparatus.
2. Description of the Related Art
Substrate processing apparatuses that carry out predetermined processing on substrates such as wafers for semiconductor devices have a processing chamber (hereinafter referred to merely as the “chamber”) in which a substrate is housed and subjected to predetermined processing. An exhaust system of the substrate processing apparatuses has a turbo-molecular pump (hereinafter referred to as the “TMP”), and a communicating pipe that communicates the TMP and the chamber together. The TMP has a rotary shaft disposed along an exhaust stream, and a plurality of rotary blades projecting out at right angles from the rotary shaft. The rotary blades rotate at high speed about a rotation axis, so that gas in front of the rotary blades is exhausted at high speed to the rear of the rotary blades. The exhaust system exhausts gas from the chamber by operating the TMP.
In the chamber of the substrate processing apparatus, particles arising from deposit attached to an inner wall of the chamber and reaction product produced during predetermined processing are floating. If these floating particles become attached to surfaces of substrates, a short circuit will occur in products such as semiconductor devices manufactured from the substrates, resulting in the yield of the semiconductor devices decreasing.
In recent years, however, it has been found that particles flow back into the chamber from the exhaust system. Specifically, it has been found that deposit attached to the rotary blades of the TMP exfoliates and flows back into the chamber, or particles exhausted from the chamber collide with the rotary blades of the TMP and recoil to directly flow back into the chamber.
It is thought that the deposit exfoliated from the rotary blades and the particles recoiled by the rotary blades are given high kinetic energy by the rotary blades rotating at high speed, and hence they repeat elastic collision with the inner wall of the communicating pipe and enter the chamber irrespective of the presence of an exhaust stream in the communicating pipe.
Regarding the backflow of particles described above, the frequency with which the TMP is replaced is increased so as to prevent particles from arising deposit exfoliated from the rotary blades (see, for example, Sato et al. “Visualization of Particles Flowing Back from Turbo Molecular Pump”, Japan Industrial Publishing Co., Ltd., Clean Technology, June 2003, pages 20 to 23).
However, because the collision of the particles and the rotary blades accidentally occur, the particles cannot be prevented from been produced even if the frequency with which the TMP is replaced is increased. As described above, the recoiled particles repeat elastic collision with the inner wall of the communicating pipe to enter the chamber and become attached to surfaces of substrates, resulting in the yield of products manufactured form the substrates decreasing.